INCREASED SATELLITE CELL APOPTOSIS IN VASTUS LATERALIS MUSCLE AFTER ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

OBJECTIVE: Recovery of the quadriceps femoris muscle after anterior ligament reconstruction is impaired. The aim of this study was to investigate satellite cell content and function of the vastus lateralis muscle after anterior ligament reconstruction. METHODS: Biopsies were obtained from the vastus lateralis muscle of 16 recreational athletes immediately before and again 12 weeks after anterior ligament reconstruction. Total satellite cell number (Pax7(+)), activated (Pax7(+)/MyoD(+)), differentiating (Pax7(–)/MyoD(+)), and apoptotic (Pax7(+)/TUNEL(+)) satellite cells, myofibers expressing myosin heavy chain (MHC) I and II, and neonatal MHC (MHCneo) were determined immunohistochemically. RESULTS: After anterior ligament reconstruction, the number of apoptotic satellite cells was significantly (p = 0.019) increased, concomitant with a significant (p < 0.001) decrease in total satellite cell number, with no change in activated and differentiating satellite cell number. MHCneo(+) myofibers tended towards an increase. CONCLUSION: Satellite cell apoptosis and the reduction in the satellite cell pool might provide an explanation for prolonged quadriceps muscle atrophy after anterior ligament reconstruction. LAY ABSTRACT Protracted muscle atrophy is common after anterior ligament reconstruction, even if athletes adhere to a structured rehabilitation programme. Satellite cells, the stem cells of skeletal muscle, play an important role in recovery of an atrophied muscle. Exercise can activate satellite cells, induce their proliferation, and probably also differentiation of these stem cells. The current study evaluated satellite cell content and function in biopsies from the vastus lateralis muscle of 16 recreational athletes immediately before and 12 weeks after anterior ligament reconstruction. After anterior ligament reconstruction, an increased number of satellite cells showed signs of apoptosis (cell death). Furthermore, total satellite cell number was decreased, with no change in the numbers of activated and differentiating satellite cells. The number of regenerating myofibers expressing neonatal myosin tended to increase. In conclusion, satellite cell apoptosis and the reduced satellite cell number might provide an explanation for the impaired muscle recovery after anterior ligament reconstruction.